Endoscopic surgery has been gaining wide acceptance as an improved and cost effective technique for conducting certain surgical procedures. In endoscopic surgery, a trocar which is a pointed piercing device, is sent into the body with a cannula placed around the trocar. After the trocar accomplishes piercing of the abdominal walls, it is removed and the cannula remains in the body. Through this cannula, endoscopic procedures are possible. Often, multiple openings are produced in the body with a trocar so that an endoscopic instrument may be placed in one cannula, appropriate viewing mechanisms placed in another cannula and fiber optics for illuminating the surgical field placed in yet another cannula. Generally, these endoscopic procedures take place under insufflation. As more is learned about endoscopic surgical procedures and more instruments developed, the type of procedures that may be performed endoscopically will increase. Presently, typical procedures are gall bladder removal, tissue repair, hernia repair and the like.
While endoscopic surgical procedures have substantial benefits to the patient, they do present certain problems to the surgeon conducting the procedure. For example, because the active part of the instrument is further removed from the manipulative part of the instrument, any slight movement of the manipulative part is magnified when it reaches the active part. Hence, when placing and forming a staple in tissue, the hand of the surgeon must be a lot steadier during the endoscopic procedure than if that same procedure was done during standard open surgery. The same can be said when severing vessels or incising tissue. Hence, in designing endoscopic surgical instruments, considerable effort is made to reduce the force required in order to operate or manipulate the instrument and allow the surgeon to have greater control over the instrument. Also, from an engineering standpoint, considerable design engineering is required to permit function of the active portion of the instrument given the physical limits of force and stroke of the surgeon's hand. Another problem in endoscopic procedures is that since the access to the surgical area is very limited, that is, through one or a few small incisions in the body, the access to the vessels, organs and tissue within the area in which the procedure is to be accomplished is very limited.
Most endoscopic instruments developed to date generate the larger forces required to drive staples through tissue and form the staples by using various mechanical levers, springs, or similar mechanical devices. Generally, a shaft extends from the handle of the instrument to the business end and linear forces are generated by this shaft through various mechanical means to drive staples through tissue or otherwise manipulate the business end of the instrument. In some instruments the shaft may be rotatable such as disclosed in U.S. Pat. Nos. 4,606,343 in order to move or position various parts of the business end with respect to each other. However, the forces required to drive staples through tissue and form the staples in the tissue are still generated by springs, levers, or other means which generate forces in a linear direction. In all instances, these forces are generated by the one manipulating the handle of the instrument and require considerable energy be exerted in order to apply the necessary forces.
Hence, it is desirable to produce endoscopic surgical instruments that can carry out a desired procedure; such as ligating vessels, stapling tissue, cutting tissue and the like, without physical restriction on the forces used to carry out these procedures and without such increased forces disrupting the operation and/or manipulation of the instrument. It is also desirable to produce endoscopic surgical instruments that allow for improved access to the surgical site; that is, the business end of the endoscopic surgical instrument may be moved about and positioned within the surgical site while still maintaining a single, small incision commonly used with such instruments.